This invention relates to a high density magnetic recording medium. The magnetic recording media now in use are generally made by mixing ferromagnetic particles with a binder vehicle and coating a nonmagnetic base with the mixture. With the spread of applications for magnetic recording, there has been a growing demand for the media capable of higher density recording.
The requirements to be met in order to realize the high density recording are understood to include the following: (1) Great coercive force of the ferromagnetic particles; (2) high intensity or amount of saturation magnetization (Is) of the ferromagnetic particles; (3) fineness of the ferromagnetic particles; (4) uniform dispersion of the ferromagnetic particles in the binder vehicle; (5) smoothness of the magnetic coating film and freedom from spacing loss; and (6) low friction resistance of the magnetic coating film. Requirements (1), (2), and (3) are met by the improvement of acicular iron oxide, use of cobalt-adsorbed or cobalt-deposited acicular iron oxide, or more recently by the introduction of acicular metallic iron.
Thorough dispersion of ferromagnetic particles in a binder vehicle has been accomplished primarily through improvements in binders and dispersing agents. In order to preclude the spacing loss that is a serious obstacle to higher density recording, the magnetic coating surface must be made smoother than heretofore. However, finishing the coating film surface smooth enough to eliminate the spacing loss between itself and the magnetic head would, in turn, increase the friction between the two. The increased friction causes stick slips between the head and the coating film, producing noise commonly known as squeal.